The present invention relates to novel polarizers more advantageously suited for quantity production than conventional polarizers and a method of manufacturing the same. More particularly, the invention relates to novel polarizers that can be easily formed on various optical elements by the oblique vapor deposition technique and a method of manufacturing the same. The invention relates also to various optical elements, such as optical isolators, equipped with the polarizers of the invention by oblique deposition, and a method of manufacturing the same.
Polarizers known in the art include dichroic polarizers, more commonly termed Polaroid plates, and birefringent polarizers. The former type, with limited extinction ratios, can hardly be used in precise measurements such as the determination of magneto-optical effects. The latter has the disadvantages of high material cost and difficulties involved in the manufacture, because a birefringent material, e.g., quartz, calcite, or magnesium fluoride, must be cut off at given angles to the axis of crystal into a prism or the like. When such polarizers are to be used in optical devices such as optical isolators, circulators, modulators, or switches, the polarizers and other component parts, e.g., Faraday rotators, must be fabricated separately. Combining and assembling these discrete elements renders it difficult to reduce the sizes of the end products. For example, conventional optical isolators require that a Faraday element be sandwiched between a pair of polarizers with their axes of transmission inclined at 45.degree. to each other, the polarizers themselves being such expensive elements as polarization prisms.
Recently a polarizer of the diffraction grating type made from LiNbO.sub.3 by proton exchange was introduced as a polarization element utilizing the diffraction phenomena (Japanese Patent Application Public Disclosure No. 63-55501). The polarizer is thin and suited for mass production, but it must use a high-priced monocrystalline substrate of LiNbO.sub.3. In addition, like the other polarizers of the prior art, it has to be fabricated independently of the optical elements to be assembled together and therefore is unable to make for the overall size reduction of the resulting optical device. Also known in the prior art is an optical isolator which is a Faraday rotator imparted with the functions of a polarizer by the formation of phase grating at a finer pitch than a half of the wavelength of light on the rotator surface (Japanese Patent Application Public Disclosure No. 2-10311). The omission of a polarization prism favors its miniaturization. On the other hand, the need of forming extremely fine grooves on the Faraday rotator with good accuracy makes the isolator difficult to manufacture and unfit for commercial production.
It is an object of the present invention to provide novel polarizers which, unlike the existing polarizers, facilitate quantity processing and reduction of space requirements and, moreover, can be attached directly and simply to the planes of various optical elements for incidence or emergence of light rays.
Another object of the invention is to provide a variety of optical elements directly equipped with such polarizers and made smaller than usual.
Still another object of the invention is to provide a method of manufacturing those polarizers.
After intensive search for the way of realizing the above objects, the present inventors have now successfully developed polarizers that utilize the diffraction phenomena and are easy to manufacture and suited for quantity production by the formation of birefringent films in a grating pattern by so-called oblique deposition.